The present invention relates to a valve which can be produced micromechanically.
In order to burn fuels in internal combustion engines such that the emissions are reduced, fuels must be injected in a controlled manner, reproducibly and reliably into the induction area or combustion chamber. The fuel is intended to be supplied via a miniaturized, controllable, robust and rapidly reacting valve, which can be produced economically, closes forming a seal without any energy being supplied (normally closed, no leak), is integrated in the injection nozzle and can be operated with a low level of electrical power. Present-day injection valves are constructed from a multiplicity of individual mechanical components and are generally composed of stainless steel. The valve is formed by a valve pin which is rounded in the shape of a hemisphere and slides into a valve seat, which is in the form of a hollow sphere. This valve is driven via electromagnetic (coils) or piezoelectric actuator drives. The precise interaction of the individually manufactured parts governs the accuracy and leakage rate of the valve. As a result of the large masses to be moved, such valves are slow and satisfy the requirements for fuel injection in modern engines only inadequately.
A microvalve is described in German patent application DE 44 2 941 A1. That valve can be produced micromechanically and it is in the form of a multilayer structure with two membranes and with a gas channel system with radially arranged channels.
The object of the invention is to provide a microvalve which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which can be produced easily and is suitable for installation in internal combustion engines.
With the above and other objects in view there is provided, in accordance with the invention, a microvalve, comprising:
a first silicon substrate formed with a valve seat having a flat edge and an outlet opening bordered by the flat edge;
a second silicon substrate permanently connected to the first silicon substrate, the second silicon substrate having a cavity and an inlet opening formed therein;
a membrane layer of polysilicon forming a membrane adjacent the cavity;
the membrane being electrically conductive and having a first side facing away from the cavity and selectively pressing against the flat edge of the valve seat for closing the valve opening;
the inlet opening and the outlet opening being bounded by the first side of the membrane opposite the cavity;
an electrode formed on a side of the cavity distal from the membrane; and
a drive circuit electrically connected to and applying a voltage between the electrode and the membrane for selectively moving the membrane into the cavity and lifting the membrane from the flat edge of the valve seat for establishing a communication between the inlet opening and the outlet opening.
In accordance with an added feature of the invention, the first and second substrates define a contact pressure between the membrane and the flat edge of the valve seat.
In accordance with an additional feature of the invention, the membrane is movably disposed above the cavity parallel to the flat edge of the valve seat.
In accordance with another feature of the invention, the membrane is disposed above the cavity and elastically deformable parallel to the flat edge of the valve seat.
With the above and other objects in view there is also provided, in accordance with the invention, a microvalve assembly formed with a plurality of individual microvalves as described above, and a common drive circuit configured to open an appropriate number of valves in dependence on a desired flow rate.
In accordance with a concomitant feature of the invention, a microvalve according as described above is integrated together with at least one sensor, and an electronic control circuit receiving a sensor signal from the at least one sensor and for driving the microvalve in dependence on the sensor signal received from the sensor.
In other words, in the microvalve according to the invention, the valve seat, with a closure part, is located between an inlet opening and an outlet opening. The valve seat essentially comprises a substrate having a connecting stub for the inlet or the outlet opening. When the valve is in the rest position, the closure part is pressed against the connecting stub. The closure part essentially comprises a micromechanical elastic membrane, preferably a part of a polysilicon layer, one side of which is pressed against the connecting stub and on whose other side there is a cavity into which the membrane can be pressed. When a gas or a liquid flows onto the side of the membrane facing the connecting stub, the membrane is lifted off the connecting stub and is pressed into the cavity, so that the gas or the liquid can flow from the inlet opening, past the edge of the connecting stub, into the outlet opening of the valve. The membrane can be stiffened by a stamp-like attachment in order to ensure that the valve opens uniformly.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a microvalve, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.